Sodium reduction combined with either a typical U.S. diet or the "DASH" diet, which is rich in vegetables, fruit, and low-fat dairy products and low in total and saturated fat, substantially lowered blood pressure in persons with high blood pressure and persons with higher than optimal blood pressure, according to the results of a study supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health.
The DASH-Sodium study found that the lowest blood pressure levels were in those eating sodium levels much lower than the currently recommended maximum of 2,400 milligrams a day while also eating the DASH (Dietary Approaches to Stop Hypertension) diet. In both the DASH diet and a typical American diet, the lower the sodium, the lower the blood pressure. The combination of following the DASH diet at the lower sodium level reduced blood pressure more than either the DASH diet or lower sodium intake alone.
These findings, which are published in the January 4 issue of the New England Journal of Medicine, were initially reported in May 2000 at the annual meeting of the American Society of Hypertension.
"The DASH-Sodium study lays to rest the long-standing controversy over whether sodium reduction lowers blood pressure in people who do not have hypertension, more commonly called high blood pressure. The study also has important implications for the treatment of hypertension, which affects almost 50 million people in this country," says NHLBI Director Dr. Claude Lenfant.
"These results challenge Americans to eat the DASH diet and to reduce sodium consumption and the food industry to reduce sodium levels in foods. Meeting this challenge, along with other lifestyle changes, could prevent the rise of blood pressure with age and allow patients to control their hypertension with fewer or even no drugs," adds Dr. Lenfant.
In the DASH-Sodium study, 412 people were randomly assigned to eat either a typical U.S. diet (the control diet) or the DASH diet, which is low in saturated fat, cholesterol, and total fat and emphasizes fruits, vegetables and lowfat dairy foods. The DASH diet is also reduced in red meat, sweets, and sugar-containing drinks. It is rich in potassium, calcium, magnesium, fiber, and protein. The DASH diet was initially used in the first DASH study, which examined the effect on blood pressure of whole dietary patterns rather than of individual nutrients. The DASH diet was found to substantially reduce blood pressure without decreasing salt intake.
In the DASH-Sodium study, investigators sought to determine the effects on blood pressure of the DASH diet at lower levels of sodium and were very interested in finding out whether sodium intakes lower than the currently recommended maximum would be even better for reducing blood pressure. The investigators also wanted to discover the combined effect of lower dietary sodium with the DASH diet and the effects of sodium reduction in certain groups of people - particularly those at increased risk but currently without high blood pressure .
Participants in the DASH-Sodium study had all of their food provided. They ate their assigned diet for 30 days at each of three sodium levels: 3,300 milligrams per day (the average level consumed by Americans); an intermediate level of 2,400 milligrams per day (the upper limit of current recommendations by the National High Blood Pressure Education Program); and a lower intake of 1,500 milligrams per day. At the start of the study, participants had systolic blood pressure (the top number in a blood pressure reading) between 120 and 159 mm Hg and diastolic blood pressure of between 80 and 95 mm Hg. These ranges are similar to about 50 percent of the U.S. adult population. About 57 percent of the study participants were women and about 57 percent were African Americans. About 41 percent of study participants had high blood pressure (defined as blood pressure over 140/90 mm Hg).
The DASH diet lowered blood pressure at each of the three levels of sodium intake. In addition, lower sodium intake resulted in lower blood pressures for those on both the typical and the DASH diets. This result applied to men, women, African Americans, whites, and those with and without high blood pressure. Neither the DASH diet nor lower levels of sodium caused undesirable effects. In fact, those on a lower sodium diet - whether control or DASH - had fewer headaches. People with high blood pressure who ate the DASH diet at the lowest sodium level had an average systolic pressure reading 11.5 mm Hg lower than participants eating the control diet at the highest sodium level. The corresponding number for participants who did not have high blood pressure was 7.1 mm Hg systolic pressure.
"The combination of eating the DASH diet at a lower sodium level is a significant effect - equal to or greater than the result you would expect from treatment with a single hypertension medication," says Dr. Frank Sacks, chair of the DASH-Sodium Steering Committee and Associate Professor of Medicine at Brigham and Women's Hospital and Harvard Medical School. "However, the long-term health benefits of the low sodium DASH diet will depend on whether the American public is willing to make long-lasting dietary changes, including choosing lower sodium foods, and whether the food industry makes available a greater number of lower sodium food products," adds Dr. Sacks.
"Following the DASH diet at the 1,500 mg of sodium level may prevent the development of high blood pressure and the increase in systolic blood pressure that typically occurs as people age," said Dr. Eva Obarzanek, the NHLBI Project Officer of the DASH-Sodium study. Other longer-term studies suggest that the benefit on blood pressure is likely to persist over the long term as long as people continue following the DASH diet and lower sodium intake, she adds.
How does one get to a daily level of 1500 mg of sodium (the equivalent of 4 grams or 2/3 teaspoon of table salt)? According to Dr. Obarzanek, the best way for people to lower sodium in their diets is to start out small with a few simple changes.
"Buy unsalted varieties of foods and condiments, take the salt away from the table, and don't use it in food preparation," she says.
A vitally important guiding principle of low-sodium eating, according to Dr. Obarzanek, is to eat fewer processed foods, a major source of sodium, or use lower sodium versions, if available. This means cutting back on regular commercially prepared frozen dinners, packaged mixes, and canned soups or broths.
To gauge the sodium level of processed foods, read nutrition labels for sodium content and the percent daily value. Dr. Obarzanek suggests choosing foods that are less than 5 percent of the daily value for sodium. You can also select foods by milligrams of sodium per serving. For example, a food with 140 mg. of sodium or less per serving is considered "low sodium," one with 35 mg sodium or less per serving is "very low sodium," and a food that has 0.5 mg sodium or less per serving is "sodium free." These are the definitions used to label food products.
To add flavor to foods, try herbs, spices, lemon, lime, and vinegar rather than salt. Good snack options include unsalted pretzels or nuts mixed with raisins, graham crackers, lowfat and fat free yogurt, plain popcorn, and raw vegetables.
Dr. Obarzanek has several suggestions for dining out. "Plan ahead and bank your sodium," she says. "If you know you're going to have a high sodium dinner at a restaurant, have a lower sodium breakfast and lunch." Other tips include "downsizing" - ordering the "kiddie" meal, which will have less sodium because it's a smaller portion; avoiding fried dishes since batter is salted; and ordering sandwiches with lettuce and tomato instead of mayonnaise, sauces and condiments.
Healthy lower-sodium eating based on the DASH diet isn't just about restrictions, according to Dr. Obarzanek. To follow this plan, people should eat 8 to 10 servings a day of fruits and vegetables (fresh, frozen, dried or unsalted canned), 7 to 8 servings of grains and grain products, and 2 to 3 daily servings of lowfat or fat-free dairy foods. The DASH diet also calls for 2 or less daily servings of meats, poultry and fish and 4 to 5 servings a week of nuts, seeds, and dry beans.
Just as with sodium reduction, making small changes is the easiest way to begin following the DASH diet. Start out by trying to have two servings of fruits and/or vegetables at each meal and as snacks. Use fruits as dessert. To increase dairy foods, try to have one low-fat or fat-free dairy serving at each meal. Treat meat as part of the whole meal, not the focus, and instead emphasize vegetables, whole grains, and dry beans.
Additional information on the DASH-Sodium Eating Plan, including a sample menu, recipes, and tips can be found on the NHLBI website at www.nhlbi.nih.gov.
To arrange an interview with Dr. Obarzanek, please call the NHLBI Communications Office at 301-496-4236. To interview Dr. Sacks, contact him at 617-432-1420.